A heat exchanger

ABSTRACT

The present invention relates to a heat exchanger unit ( 13 ) for exchanging heat between a first fluid and a second fluid. The unit ( 13 ) comprises a flow passage for the first fluid and a flow passage for the second fluid, the flow passages are connected to inlets ( 9 ) and outlets ( 10 ) of the heat exchanger unit ( 13 ) through which the first and the second fluid flow into and out of the heat exchanger unit ( 13 ). The unit ( 13 ) further comprises one or more heat transferring elements ( 1 ) having a first fluid contact surface and a second fluid contact surface through which surfaces heat is conducted from the first to the second fluid or vice versa, the contact surfaces form at least part of the flow passages, The unit ( 13 ) further comprises one or more total pressure increasing means ( 8 ) for increasing the total pressure of at least one of the fluids at least locally in the heat exchanger unit ( 13 ), and a casing ( 12 ) encapsulating the one or more heat transferring elements ( 1 ) and one, some or all of the one or more total pressure increasing means ( 8 ).

The present invention relates to an apparatus and a method for exchanging heat between at least two fluids. The invention relates in particular to a heat exchanger unit for exchanging heat between a first fluid and a second fluid, which unit comprises preferably one or more heat transferring elements having a first fluid contact surface and a second fluid contact surface through which heat is conducted from the first to the second fluid or vice versa, one or more total pressure increasing means for increasing the total pressure of at least one of the fluids at least locally in the heat exchanger unit, and a casing encapsulating the one or more heat transferring elements and the one or more total pressure increasing means. The invention furthermore relates to heat transferring elements, heat exchangers comprising such heat transferring elements and a cassette comprising at least one or more heat transferring elements.

BACKGROUND OF THE INVENTION

Heat exchange between fluids takes place in a number of processes. Typically, the fluids are separated from each other by an interface being impenetrable for the fluids in question, and the heat transfer from one fluid to the other occurs through this impenetrable interface. The heat transfer rate is strongly coupled to the velocity of the fluids flowing past the interface and in particular the velocity in the boundary layer close to the interface. Furthermore, in order to increase the heat transfer rate, the surface of the interface may be given certain characteristics such as being corrugated.

In many practical implementations of heat exchanger units, the heat exchanger unit represents a pressure loss that need to be compensated for to enable the fluid to flow through the unit. This is typically done by assigning one or more pumps to drive the fluid through the unit. A heat transfer system is accordingly assembled by connecting a number of stand-alone units, such as one or more pumps and one or more heat exchanger units by use of pipes, flanges and the like.

Each such connection typically represents a loss in pressure, e.g. due to a change in flow cross section. A connection may furthermore be subjected to sealing problems e.g. where the piping and the stand alone units are connected to each other.

In FIG. 1 a which shows schematically a commonly known heat exchanger system, the various fluid dynamic processes are indicated in systems connected by use of pipes, flanges and the like. The processes are illustrated at three levels of details with increasing detailing from top to the bottom of the figure. At the very bottom of the figure, a graph showing the pressure of the fluid is indicated. Ptot refers to total pressure, Pstat refers to static pressure and Pdyn refers to dynamic pressure.

As indicated in FIG. 1 a, a pump (P) is provided upstream and connected to the heat exchanger unit (HE) by a pipe, and the impeller increases the pressure and in particular the dynamic pressure. The dynamic pressure is converted into static pressure in a diffuser of the pump. In the example indicated in FIG. 1 a, the fluid with high static pressure is fed into a heat exchanger in which the velocity of the fluid is increased due to a decrease in cross sectional area. Thereby the static pressure decreases and the dynamic pressure increases. Such conversions from dynamic pressure to static pressure to dynamic pressure result in losses which in general must be balanced by e.g. electrical power for driving a motor of the pump; such losses are energy consuming and thereby undesirable.

US 2006/0254752 discloses a radiator including: an inlet header having a hollow shape and being provided with an inlet for a coolant to enter; a plurality of flat tubes connected to the inlet header at one end; and an outlet header having a hollow shape and being provided with an outlet for the coolant to discharge, the outlet header connecting to another end of the plurality of flat tubes. The plurality of flat tubes form channels for the coolant and connect the inlet header and the outlet header. While the invention disclosed therein may provide some advantageous effect it does not seem to provide much flexibility as to design and relies heavily on one of the fluids being air.

Furthermore, commonly known heat transfer systems typically have a relatively long response time before full heat transfer between two or more fluids is established. In households this often means that tap water flowing through such units initially does not reach the desired temperature and are therefore not used.

Additionally, commonly know heat exchangers seem have to have an upper heat transfer limit of 4000 W/m²K which limit might be linked to the use of connecting stand alone unit (pumps and heat transfer unit).

Thus, it is an aim of the present invention to seek to at least mitigate the problems occurring in heat transfer system being assembled from stand alone units by pipes, flanges and the like.

DISCLOSURE OF THE INVENTION

The above described loss related to converting dynamic pressure into static pressure is in many of the preferred embodiments of the present invention reduced or even avoided by arranging an impeller immediately upstream of heat exchanging surfaces as indicates in FIG. 1 b. FIG. 1 b is structured in way similar to FIG. 1 a and shows that the impellers increases the total pressure and no conversion of pressure takes place before the fluid gets into contact with the heat transferring elements.

In connection with the present invention, it has been found that e.g. the rotational nature of fluid flowing out of an impeller of a centrifugal pump may have positive effect on the heat exchange rate between the fluids. In systems assembled from stand alone units, such as pumps and heat exchanger units, by use of pipes, flanges and the like, the effect linked to a rotational component of one or more of the fluids is only obtained with great difficulties as the various pipes, flanges and the like will have a tendency to remove the rotational component in the fluids.

The present invention relates in a first aspect to a heat exchanger unit for exchanging heat between a first fluid and a second fluid, the unit comprising preferably

-   -   a flow passage for the first fluid and a flow passage for the         second fluid, the flow passages are connected to inlets and         outlets of the heat exchanger unit through which the first and         the second fluid flow into and out of the heat exchanger unit,     -   one or more heat transferring elements having a first fluid         contact surface and a second fluid contact surface through which         surfaces heat is conducted from the first to the second fluid or         vice versa, the contact surfaces form at least part of the flow         passages,     -   one or more total pressure increasing means for increasing the         total pressure of at least one of the fluids at least locally in         the heat exchanger unit,         and     -   a casing encapsulating the one or more heat transferring         elements and one, some or all of the one or more total pressure         increasing means.

Thus, by use of heat exchanger units according to the present invention, the temperature of the first and second fluids will be different when they leave the heat exchanger unit via outlets compared to when they enter the heat exchanger unit via inlets. Inside the heat exchanger unit, the total pressure of at least one of the fluids is increased at least locally by total pressure increasing means.

In preferred embodiment, the total pressure increasing means provide(s) a rotational flow in at least one of the fluids which rotational flow has been found to have a positive effect on the heat exchange between the fluids.

In accordance with preferred embodiments of the present invention, a heat exchanger unit has a casing which preferably may be considered as a container like structure inside which one or more heat transferring element(s) and one or more total pressure increasing means are arranged. Thereby the need for connecting stand-alone units by pipes to provide a heat exchanger unit may be avoided and a compact unit providing a good possibility to meet a given heat exchanging demand may be provided.

The heat exchange between the fluids will typically result in a pressure loss e.g. due to a flow path including bends and the like, and the total pressure increasing means is/are preferably used to overcome at least the pressure loss resulting from at least one of the fluids flowing through the heat exchanger unit.

Thus, while the known heat exchanger units are assembled by connecting a number of stand-alone units via pipes, the present invention is designed so that it preferably comprises a pressure carrying casing inside which the heat transferring elements and total pressure increasing means are arranged, whereby the unit may be made more compact and efficient. The efficiency of the unit may furthermore be increased as the number of heat transferring elements may be chosen so that a given demand may be matched more accurately than by building a heat exchanging unit from a number of stand-alone units.

In the present disclosure, a number of terms are used. Although these terms are used in a manner ordinary to a person skilled in the art, a brief explanation of some of these terms will be presented below.

Fluid is used to designate at least a liquid, a gas, a fluidized medium or combinations thereof.

Flow passage is preferably used to designate the hollow space through which a fluid flows within the heat exchanger unit. The flow passage preferably comprises one or more channels which channels may be arranged in parallel and/or in series. Typically, the channels comprise fluid contact surfaces through which the heat is conducted.

Casing is preferably used to designate the wall of the heat exchanger unit which wall confines fluid in the heat exchanger unit so that fluid may flow out of and into the processing unit through one or more inlets and outlets provided in the casing. Thus, the casing thereby preferably forms a sealed encapsulation of the heat exchanger unit. The casing may preferably comprise a number of wall elements. At least part of the casing may preferably constitute a part of the flow passages of the heat exchanger.

Cassette is preferably used to designate an element which either contains one or more heat exchanger elements, is adapted to receive one or more heat transferring elements or both. A cassette typically comprises an outer housing arranged so as to form at least part of the casing, one or more inlets and one or more outlets. The outer housing may preferably be pressure carrying in the sense that no further casing is needed to withstand the pressure difference between the interior and exterior of the cassette. Furthermore, the outer housing typically and preferably contributes in defining the flow passage through the unit. A cassette is shaped so that it comprises one or more flow passages through the cassette from its inlet to its outlet—which one or more flow passages form part of one or more of the flow passages in the unit. The inlet(s) and outlet(s) of cassettes are preferable provided so that when two cassettes are combined, the outlet(s) of one cassette is/are directly connected to the inlet(s) of the other cassette and vice versa. “Directly connected” is preferably used to designate a situation where the velocity and pressure of the fluid flowing out of the outlet is the same as the velocity and pressure of the fluid flowing into the inlet, which e.g. may be provided by connecting the outlet and inlet with each other with no intermediate piping in between. Furthermore, when two or more cassettes are combined, the outer casings of the cassettes are preferably combined to form at least part of the pressuring carrying casing of the processing unit. Furthermore, as a cassette often comprises total pressure increasing means overcoming the pressure loss due to fluid flowing though the cassette, the assembled unit may often be pressure neutral to the process in which it is to operate. Additionally, when total pressure increasing means is present in the cassette, the cassette is preferably designed, so that flow of at least one of the fluids through the cassette is pressure neutral or the pressure of the fluid in question flowing through the cassette is even increased.

Total pressure increasing means is preferably used to designate an element increasing the total pressure (stagnation pressure) of a fluid. A total pressure increasing means preferably is or comprises a fluid velocity inducer, such as an impeller.

Fluid velocity inducer is preferably used to designate an element inducing velocity to the fluid so that its direction and/or total pressure is changed. A fluid velocity inducer is preferably an impeller.

Inlet/outlet is preferably used to designate a cross section or a region where fluid flows into or out of an element or unit. The inlet/out may preferably be an end cross section or a region of a pipe, channel or the like. Inlet and outlet may preferably also be considered as the sections of a control volume through which fluid flow into the element/out of the element which control volume encircling the element or unit in question.

In accordance with many of the preferred embodiment of the present invention, heat transfer occur at locations where the fluids have relatively high velocities and at least one or both fluids typically also flow in a swirling motion; both flow patterns are found to be beneficial to the heat transfer rate.

Depending on the actual use, the unit may be configured so that either one or both of the fluids may be pumped through the unit by total pressure increasing means arranged inside the unit. Therefore, the present invention typically provides a compact heat exchanger unit which may be adapted to be pressure neutral for the process in the sense that no further pressurisation means, such as pumps, is needed to drive the fluid(s) through the unit.

Furthermore, heat exchanger units according to the present invention are found to be easily scalable to meet a given heat transfer demand. For instance, the unit may be configured by arranging a number of heat transferring elements which in common meets the heat transfer demand in a casing into which the heat elements fits; or the unit may be configured by stacking a number of cassettes containing a number of heat transferring element.

In preferred embodiment, the heat transferring element(s) may preferably be plate shaped and comprise fluid channels forming part of the flow passages for the first and the second fluids. These channels preferably extend from one side of the heat transferring element to the other side of the heat transferring element. Thereby, the first and the second fluid flow from one side of the heat transfer element to the other side through the heat transfer element.

Preferably, the first fluid contact surface of each heat transferring element may be an inner surface of at least one channel provided in the heat transferring element, which channel has a channel inlet and a channel outlet.

Heat exchanger units according to the present invention may preferably comprise a stack of at least two heat transferring elements which are connectable so that the first fluid flows from the channel outlet of one heat transferring element to the channel inlet of the consecutive heat transferring element.

Preferably, the outlet of one channel may be connected or connectable to the inlet of the consecutive channel via connection stubs, so that the first fluid may flow from an inlet pipe to a first heat transferring element via connection stub(s) and from a last heat transferring element to an outlet pipe via connection stub(s).

In preferred embodiments of the heat exchanger unit, the first fluid may preferably be pumped through the heat transferring unit by a pump arranged outside the casing of the heat exchanger unit.

The heat transferring element(s) may in many preferred embodiment be substantially disc-shaped (not necessarily having an circular outer rim) and comprise a hole, preferably being centrally arranged, wherein the at least one total pressure increasing means is placed in such a way that it transports the second fluid flow from one side of the heat transferring element to the other.

In preferred embodiments, the heat transferring element may comprise a guide plate forming a channel leading the second fluid towards the total pressure increasing means.

Preferably, at least a part of the casing forms a part of the flow passage for the second fluid.

The one or more of the total pressure to increasing means may preferably be adapted to increase the pressure of the second fluid to an extent at least partially overcoming the pressure loss due to fluid flowing through the heat exchanger unit. Additionally, the one or more total pressure increasing means may be adapted to increase the pressure of the second fluid to an extent at least overcoming the pressure loss due to the fluid flowing through the heat exchanger unit.

Preferably, the total pressure increasing means may comprise or may be constituted by one or more fluid velocity inducers. One, more or all of the fluid velocity inducers may preferably be adapted to receive one of the fluids at one velocity and deliver the fluid at a higher velocity.

One or more of the fluid velocity inducer(s) may preferably be arranged relatively to second fluid contact surface so that the dynamic pressure of the second fluid is substantially the same when the fluid initially contacts the second contact surface as when the fluid leaves the fluid velocity inducer.

Preferably, one or more, and in some embodiments all, of the one or more fluid velocity inducers may preferably be impellers. The impeller(s) may preferably be /impeller(s) with a motor-driven rotational motion. In preferred embodiments, the impeller(s) may preferably be mounted on a motor-driven shaft in such a way that the axis of rotation of the shaft and the impellers are coincident.

The casing may preferably be a pressure carrying casing adapted to resist the pressure difference between the pressure of the fluids in the heat exchanger unit and the pressure outside the heat exchanger unit. In preferred embodiments, the casing or at least a part thereof may be tubular shaped.

The casing may preferably comprise a pressurization stage preferably comprising one or more impellers, said pressurisation stage being placed so that at least one of the fluids passes there through before it flows to the one or more heat transferring element(s).

A number of heat transferring elements may preferably be stacked with a distance between each heat transferring element so as to provide channels between two neighbouring elements, the channels being at least a part of the flow passages for the first and the second fluid and surfaces of the heat transferring elements facing towards the channels constitute at least a part of the fluid contact surfaces, each heat transferring element is at its rim preferably sealed to a casing and the unit comprising a number of connection stubs allowing fluid to flow from one channel to a channel located upstream of a neighbouring channel. Total pressure increasing means may preferably be arranged in one or more channel(s) and the heat transferring elements may preferably be disc shaped (not necessarily having a circular outer rim).

The heat transferring elements may in general be adapted to be rotated.

At least a part of the surface of the first fluid contact surface and/or the second fluid contact surface may preferably be manufactured to have a roughness being smooth or rough. A surface is typically considered smooth when the rms value of the height k of roughness elements is small compared to the thickness of the viscous wall layer i.e. k⁺=U_(t) k/v<1. Alternatively or in combination therewith, at least a part of the first fluid contact surface and/or the second fluid contact surface may be corrugated.

The material(s) of the heat transferring elements may preferably be selected from metal, composites materials, coated material, plastic, ceramics or combinations thereof.

In preferred embodiments of heat exchanger units according to present invention, the unit may preferably comprising one or more cassettes each containing a number of heat transfer element. In combination therewith, an outer housing of one or more of the cassettes may form at least a part of an outer surface of the casing. Alternatively or in combination therewith, an outer housing of one or more of the cassettes forming at least a part of the casing may preferably abut an interior surface of the casing.

One or more of the cassettes may preferably comprise total pressure increasing means.

One or more of the cassettes may be adapted to maintain and/or provide a rotating flow, such as a swirling flow, in at least a part of one or both flow passages.

One or more of the cassettes may preferably be adapted to receive or the cassette may comprise a fluid velocity inducer, the fluid velocity inducer constituting at least a part of one or both flow passages. The fluid velocity inducer may preferably be adapted to receive fluid at one velocity and deliver the fluid at a higher velocity.

In preferred embodiments of the invention, the first and the second fluid contact surfaces may preferably be impermeable to fluid.

In preferred embodiments of heat exchanging units according to present invention, at least a part of the flow passages comprising the contact surfaces may preferably extend in a curved manner in one geometrical plane.

Heat exchanger units according to the present invention may preferably be adapted to provide a rotating flow, such as a swirling flow past at least one or both contact surfaces.

The total pressure increasing means may in preferred embodiments be adapted to increase the total pressure of the fluid(s) flowing through the unit, so that the fluid(s) leaving the unit has(have) a higher total pressure than when the fluid(s) flows into the unit.

In a second aspect, the present invention relates to a heat transfer element preferably comprising a first fluid contact surface and a second fluid contact surface through which surfaces heat is conducted from the first to the second fluid or vice versa, wherein

-   -   the first contact surface is an inner surface of at least one         channel provided in the heat transferring element, which channel         has an inlet and an outlet,     -   the second contact surface is at least a part of the outer         surface of the at least one channel being provided in the heat         transferring element.

The heat transferring element may preferably be substantially disc-shaped (not necessarily having a circular outer rim) and may preferably comprises a hole, preferably being centrally arranged, wherein at least one total pressure increasing means preferably can be arranged in such a way that it transport a fluid from one side of the heat transferring element to the other.

Heat transferring elements according to the second aspect of the invention may preferably one or more the features disclosed above in relation to the first aspect of the invention.

In a third aspect, the present invention relates to a cassette comprising one or more of the features disclosed in connection with the first and/or the second aspect of the invention.

In a fourth aspect, the invention relates to a method of exchanging heat between a first and a second fluid, the method preferably comprising feeding fluids to a heat exchanger unit according to the above disclosed aspect of the invention.

The present invention, and in particular preferred embodiments thereof, will now be described in greater details with reference to the accompanying drawings in which:

FIG. 1 a shows schematically a commonly known heat exchanger system and FIG. 1 b shows schematically flow in heat exchangers according to preferred embodiments of the present invention,

FIG. 2 shows a heat transferring element of a heat exchanger unit according to an embodiment of the present invention; the heat transferring elements are seen obliquely from above (FIG. 2 a) and below (FIG. 2 b), respectively.

FIG. 3 is a schematic illustration of a stack of heat transferring elements of a heat exchanger unit according to a preferred embodiment of the present invention. For clarity the elements are shown spaced apart, whereas in practise they abut each other mutually as shown in FIG. 7. Furthermore, a part of the casing has been removed to render the heat transferring elements visible.

FIG. 4 shows the heat transferring elements of FIG. 3 seen obliquely from below and with the casing removed for clarity.

FIG. 5 illustrates the flow path of the first fluid flowing in the channels of the heat transferring elements shown in FIG. FIG. 3.

FIG. 6 illustrates the flow path of the second fluid flowing between the heat transferring elements shown in FIG. 3.

FIG. 7 shows an embodiment of a section of a heat exchanger unit according to the present invention. FIG. 7.a is a top view, and FIG. 7.b is a sectional view along line A-A in FIG. 7.a.

FIG. 8 shows schematically a side view of a heat exchanger unit according to the present invention.

FIG. 9 shows schematically a cross sectional view of a part of a heat exchanger unit according to the present invention with a pressurisation stage for pumping one of the fluids through the heat exchanger unit.

FIG. 10 shows an exploded view of an embodiment of a section of heat exchanger unit with impellers for pumping two fluids through the unit according to the present invention, the unit comprising impellers for pumping the two fluids through the unit.

FIG. 11 shows schematically an embodiment of a heat exchanger according to the present invention wherein the unit is made from a number of cassettes,

FIG. 12 shows a cross sectional view of the heat exchanger unit shown in FIG. 11,

FIG. 13 shows an exploded view of a preferred embodiment of a section of a heat exchanger unit according to the present invention for exchanging heat between three fluids, the unit comprising impellers for pumping the three fluids through the unit,

FIG. 14 shows an exploded view of a further embodiment of a section of a heat exchanger unit according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

A heat exchanger unit 13 (see FIG. 8) according to a preferred embodiment of the present invention comprises at least one and preferably a larger number of heat transferring elements 1 which may have a design as illustrated in FIG. 2. FIG. 2.a and FIG. 2.b show the heat transferring element 1 seen obliquely from above and from below, respectively; “above” and “below” refers to the orientation of the heat exchanging unit in FIG. 7. The heat transferring elements 1 have channels 2 for guiding a first fluid along a first fluid contact surface which is the internal surface of the channel 2 and therefore not directly visible in the figure. As it appears from the figure, the channel 2 extends in a curved manner in one geometric plane. Each channel 2 comprises a channel inlet 3 through which the first fluid enters the channel 2 and a channel outlet 4 through which the first fluid exits the channel 2. The channel outlet 4 and channel inlet 3 comprise fluid guides in form of connection stubs 5 (see FIG. 3) which are connectable so that the heat transferring elements 1 are stackable, and the first fluid can flow from a channel 2 of one heat transferring element 1 to a channel 2 of a consecutively arranged heat transferring element 1. This is described in more detail below. The heat transferring elements 1 preferably abut and thereby support each other at support bosses 6, but it is also possible within the scope of the invention that they only abut at the channel inlets and outlets (3, 4). The heat transferring element 1 comprises a central hole 7 for placing an impeller 8 (see FIG. 4), the function of which is described below.

FIG. 3 shows a stack of three heat transferring elements 1 together with the inlet and outlet pipes 9, 10 for the first fluid. For clarity, the heat transferring elements 1 are shown spaced apart and the impellers 8 being removed (see FIG. 4), whereas in practise they abut each other mutually as shown in FIG. 7. The rims 11 of the heat transferring elements 1 abut a circumferential casing 12 and are preferably sealed to the casing at the rims 11. In the figures, a part of the casing 12 has been removed to render visible the heat transferring elements 1. For more details on the casing 12, please refer to FIG. 8 and the description thereof.

Fluid velocity inducers in the form of impellers 8 are arranged along a rotatable common shaft (not shown; see FIG. 9) so that when the shaft is rotated, typically by a motor (not shown; see FIG. 8), the impellers 8 transport a second fluid from the bottom (relatively to the orientation of the figure) to the top of the heat exchanger unit 13. The fluid velocity inducers increase the total pressure of the fluid flowing through the fluid velocity inducers. When the second fluid leaves an impeller 8, the second fluid contacts the second fluid contact surface of the heat transferring element 1, this surface being the outer and thereby directly visible surface; i.e. visible in the figure.

FIG. 4 shows the heat transferring elements 1 of FIG. 3 seen obliquely from below and with the casing 12 removed for clarity and with impellers mounted. In the embodiment shown, a guide plate 14 has been mounted to the channel 2 of each heat exchanger element 1 to guide the second fluid towards the impellers 8. In an alternative embodiment, this guide plate 14 is made integral with the remaining heat transferring element 1.

The flow passage of the first fluid through the heat exchanger unit 13 of FIGS. 3 and 4 is illustrated by a broken line in FIG. 5. It enters the heat exchanger unit 13 through an inlet in form of an inlet pipe 9 from where it flows to the channel 2 of the upper heat transferring element 1 via one or more connection stubs 5. The first fluid flows through the consecutive heat transferring elements 1 as illustrated, and from the last heat transferring element 1, it flows out through an outlet in form of an outlet pipe 10. The flow of the first fluid is typically caused by a pump (not shown) placed external to the heat exchanger unit 13, but the pump may also be integrated in the heat exchanger unit 13 e.g. in a manner similar to what is disclosed in FIG. 9 (pressurisation stage 25) or as shown in FIG. 10. As mentioned, the first fluid exchanges heat/energy with a second fluid flowing between the heat transferring elements 1, i.e. along their second fluid contact surfaces.

The flow passage of the second fluid is illustrated schematically in FIG. 6. The second fluid enters the central region of the first impeller 8 which is rotatable e.g. by means of a motor driven shaft (not shown; see FIG. 8, 9). The centre axis of the shaft is coincident with the centre axis of the impellers 8, and the second fluid preferably flows towards the impellers 8 along the whole periphery of the shaft. This is indicated with one central arrow in the figure for illustrative purposes only. The rims 11 are sealed to the casing so as to define a channel between two neighbouring heat transferring elements 1.

The impeller 8 induces energy to the second fluid which makes it flow towards the rim 11 of the heat transferring element 1. From here it flows into the space partly defined by the guide plate 14. This flow is mainly obtained by a draw from the impeller 8 placed in the consecutive heat transferring element 1, and from there the flow pattern is repeated.

The figures described above show that the first and second fluids flow in opposite overall directions, i.e. upwards and downwards with respect to the figures. It is however also possible within the scope of the invention to have the two fluids flowing in the same overall direction.

Thus, as shown inter alia in FIGS. 5 and 6, the heat transferring elements 1 are plate shaped elements having channels for the first and the second fluid respectively forming part of the flow passages for the first and the second fluids and extending from one side of the heat transferring element to the other side of the heat transferring element so that the first and the second fluid can flow from one side of the element to the other. One of the channels is the channel 2 with channel inlet 3 and channel outlet 4, and another channel is defined by the space partly defined by the guide plate 14, the hole 7 and, if arranged, the impeller 8.

FIG. 7 shows a section of an embodiment of a heat exchanging unit 13 according to the present invention. In FIG. 7.a the section of the heat exchanging unit 13 is seen from above, and FIG. 7.b is a sectional view along line A-A in FIG. 7.a. The channel 2 of the last heat transferring element 1 is slightly longer than the others, since this channel 2 is connected to the outlet pipe 10 as illustrated in FIG. 7.b. The section of the heat exchanger unit 13 is shown integrated with casing elements 17, 19 comprising inlet 15 an outlet 16 for the second fluid in FIG. 8.

The flow of the second fluid along the second fluid contact surface has a radial and a tangential velocity component. Furthermore, the second fluid flowing out of the impeller comes in direct contact with the second fluid contact surface with no conversion of dynamic pressure into static pressure before contact between the surface and fluid is made.

FIG. 8 shows a preferred embodiment of a heat exchanger unit according to the present invention. The heat exchanger unit 13 comprises a casing 12 having three casing elements, a first casing element 17, an intermediary casing element 18, and a second casing element 19. The term “intermediary” is used as a reference to the location of the element namely between the first casing element 17 and the second casing element 19.

The heat transferring elements 1 are arranged inside the intermediary casing element 18 which is shaped as a cylinder with open ends. The inlet and outlet pipes 9, 10 leading the first fluid to and from the heat transferring elements 1 extend through the wall of the first casing element 17 as indicated in FIG. 8. The first casing element 17 further comprises an outlet 16 for the second fluid arranged in a first protrusion 20 of the first casing element 17. A fixture 21 for connecting a motor 22 to the unit is placed on the first protrusion 20. The motor 22 is used to drive the impellers 8 arranged inside the heat exchanger unit 13, which impellers 8 are arranged on a shaft 23 extending from the motor 22 through the wall of the protrusion 20 and typically into but not through the second casing element 19.

The second casing element 19 comprising an inlet 15 for the second fluid as indicated on FIG. 8 and leads the second fluid to the heat transferring elements 1 arranged in the intermediary casing element 18.

The heat exchanger unit shown in FIG. 8 is assembled by inserting the intermediary casing element 18 into the first and the second casing elements 17, 19 as indicated in FIG. 9. Sealing between the intermediary casing element 18 and the first and the second casing element 17,19 respectively may be accomplished by arranging seals such as o-rings (not shown) in grooves (not shown) in surfaces abutting each other.

In preferred embodiments of the invention, the casing 12 is a pressure carrying casing adapted to resist the pressure difference between the pressure of the fluids 15 in the heat exchanger unit 13 and the ambience pressure, i.e. the pressure outside the heat exchanger unit 13.

If desired, it is possible within the scope of the invention to ensure that the pressure of the second fluid is increased inside the heat exchanger unit 13 before it flows through the heat transferring elements 1. Such an increase in pressure can e.g. be established as illustrated in FIG. 9 which shows a cross sectional view of a detail of a heat exchanger unit 13 according to the present invention. The detail shown comprises a part of the intermediary casing element 18, the second casing element 19, and four stacked heat transferring elements 1 with impellers 8. The second casing element 19 has a second protrusion 24 comprising a pressurisation stage 25 with three impellers 8 and a shaft 23 on which all impellers 8 are arranged. The shaft 23 is rotated by a motor 22 arranged as indicated in FIG. 8. The pressurisation stage may preferably be used to pressurise the fluid more than what is need to overcome the loss due to the flow through the heat exchanging unit.

FIG. 10 shows a further embodiment where both fluids are pumped through the unit 13 by use of internally placed impellers 8; the figure shows the embodiment in an exploded view with the heat transferring elements 30 spaced apart and the casing except the end casings parts 12 a, 12 b removed to render the interior of the heat transfer unit visible. The heat exchanger unit 13 comprises a number of heat transferring elements 30 formed as discs. Please note that in the present context the use of “disc” does not necessarily imply a circular structure; on the contrary and as indicated in FIG. 10 discs may e.g. have an octagonally shaped perimeter. Consequently, the heat transferring elements 30 may be described as plate shaped. The heat transferring elements are stacked so as to provide channels 31 between neighbouring elements 30 as shown in the figure. By this configuration, the surfaces of the heat transferring elements 30 facing towards a channel constitute the fluid contact surfaces for the first and the second fluid respectively.

Connection stubs 32 leading fluid from one channel 31 to another channel 31 located upstream of a neighbouring channel are provided; as shown in the figure these may be arranged on some of the elements or be separate pieces to be fitted into a mating connection provided in the elements 30. The connection stubs 32 connect to hole 32 a in a neighbouring heat transferring element 30. Each heat transferring element 30 abuts the casing at the rims 33. The rims 33 are preferably sealed to the casing.

The flow paths of the two fluids are indicated FIG. 10, wherein it is shown that the first fluid enters into the heat exchanger unit 13 from below (with reference to the orientation of FIG. 10) through an inlet stub and flows through a connection stub 32 into a channel 31 being connected via a connection stub 32 to into an impeller 8. After the total pressure has been increased in the first fluid by the impeller 8, the fluid flows in a swirling motion towards and through a connection stub 32 (it should be noted the flow may be straightened out when flowing through connection stubs 32) and enters into the next channel 31. In this next channel the fluid flows towards and through a next connection stub 32 which leads to an impeller. This pattern may be repeated a number of times by stacking more heat transfer elements 30, before the first fluid flows out of the unit through an outlet stub.

The second fluid flows into the heat exchanger unit via an inlet stub from above and via a connection stub 32 to an impeller 8. After the impeller 8, the second fluid flows in a swirling motion into a channel 31 towards a connection stub leading fluid to a next channel 31. The fluid flows through the next channel 31 towards and through a connection stub 32 leading the fluid to an impeller 8. The pattern may be repeated a number of times by stacking more heat transfer elements, before the second fluid flows out of the unit through an outlet stub.

As can be realised from FIG. 10, a channel in which the first fluid flows is arranged between channels 31 through which the second fluid flow (or vice versa depending from which fluid the situation is seen) and as the fluids have different temperatures, heat exchange between the fluid through the heat transferring elements 30 occur.

The embodiment shown in FIG. 10 is shown to have a octagonal cross section when viewed from above. However, the cross section may be given other shapes such as squared or circular. The outer casing 12 is preferably made as a tube with end casing parts in form of plates arranged at both ends of the tube as indicated in FIGS. 10 as 12 a and 12 b. The end casing parts comprise connection stubs serving as inlets/outlet through which the first and the second fluids are fed into and flows out of the unit and may e.g. be shaped as indicated in FIG. 8. The end casing part also comprises penetrations though which shafts 23 on which the impellers are arranged extend. Suspension of the shafts 23 may be provided by a bearing 47 (see FIG. 12 for an example on this) arranged in the end casings, and seals are provided between the shafts 23 and the end casing where the shafts 23 extends through the casing to avoid fluid leaking out of the unit.

Preferred embodiments of the present invention may be embodied in a manner where the heat exchanger unit is made up from a number of cassettes. Such a cassette will typically comprise a number of heat transferring elements, and the cassettes are adapted to be combined, typically stacked, to form a heat exchanger unit. One such example is shown in FIG. 11. In other embodiments, one or more cassettes comprising heat transferring elements are combined with cassettes comprising other means for interacting with the fluid.

FIG. 11 shows schematically a heat exchanger unit according to the present invention. The unit shown in FIG. 11 is formed as an elongated unit having cylindrical outer casing 12 and comprising five cassettes 40, an inlet element 41 (similar to the second casing element 19 in FIG. 8), an outlet element 42 (similar to the first casing element 17 in FIG. 8) and a motor 22. The motor 22 is arranged on a fixture 21. In the embodiment shown in FIG. 11, the casing comprises the outer housings of cassettes 40, the inlet element 41 and the outlet element 42.

Within the cassettes 40 a number of heat transferring elements 1 and impellers 8 (see e.g. FIG. 4) are arranged which impellers 8 are arranged on a common shaft 23 extending from the motor 22 to a bearing (see FIG. 12) arranged in the inlet element 41 so that when the motor 22 rotates, it rotates all the impellers 8.

The second fluid enters into the heat exchanger unit 13 through the inlet 15 (see FIG. 11) provided in the inlet element 41, flows through the heat exchanger unit 13 and leaves the heat exchanger unit 13 through the outlet 16 (see FIG. 11) provided in the outlet element 42.

One of the cassettes 40 comprise connections which are the ends of the pipes 9 10 and 10 shown in FIG. 3.

FIG. 12 shows schematically a longitudinal cross section of a heat exchanger unit 13 according to the present invention, and shows in particular one way of assembling the unit shown in FIG. 11. The unit is formed as an elongated unit having a cylindrical casing and comprises six cassettes 40, an inlet element 41, an outlet element 42 and a motor 22 arranged on a fixture 21 with a shaft 23 for rotating impellers (not shown) arranged in the heat exchanger unit 13. Heat transferring elements 1 as well as impellers 8 are not shown in the figure. The outer housings of the inflow element 41 and the outflow element 42 are considered as part of the casing 12.

In the embodiment illustrated in FIG. 12, the cassettes 40 and elements 41, 42 are assembled by a heat exchanger unit assembling fixture comprising a number of stay bolts 43 extending along the longitudinal direction of heat exchanger unit 13 and penetrating clamps 44. Nuts 45 are provided at the ends of the stay bolts 43 so that when the nuts 45 are tightened, the clamps 44 will provide a longitudinal force to the heat exchanger unit 13 so that the elements 41, 42 and cassettes 40 are held together in the longitudinal direction.

Securing of the elements 41, 42 and cassettes 40 in a direction perpendicular to the longitudinal direction of the heat exchanger unit 13 is shown as being provided by ring shaped guides 46 into which the elements 41, 42 and cassettes 40 fit snugly. Sealing of the heat exchanger unit is provided by applying o-rings e.g. in grooves provides in the ring shaped guides 46.

A structure of the heat exchanger unit comprising cassettes may also be applied to the heat exchanger unit shown in FIG. 10.

The surface of the fluid contact surfaces of the heat transferring element may be manufactured to have a selected character. Typically, the roughness of the fluid contact surfaces may be made smooth, rough and/or the surfaces may be corrugated. A surface is typically considered smooth when the rms value of the height k of roughness elements is small compared to the thickness of the viscous wall layer i.e. k⁺=U_(t) k/v<1.

Furthermore, the material of the heat transfer elements may be selected from materials having particular characteristics as to heat transferring coefficient and/or resistance against e.g. chemical exposure to avoid e.g. corrosion of the heat transferring elements.

The embodiments shown herein have so far focussed on exchanging heat between two fluids. However, the invention may also be applied to exchanging heat between more than two fluids. This may be accomplished e.g. by arranging the heat transferring elements 1, 30 and connection stubs 5, 32 so as to lead fluids to channels where the neighbouring channels contains the fluids with which the fluid is to exchange heat with. Such an example is shown in FIG. 13.

FIG. 13 shows an embodiment where three fluids are pumped through the unit 13 by use of internally placed impellers 8; the figure shows the embodiment in an exploded view with the heat transferring elements 30 spaced apart and the casing except the end casings parts 12 a, 12 b removed to render the interior of the heat transfer unit visible. The end casing parts 12 a, 12 b may e.g. be shaped as indicated in FIG. 8. The heat exchanger unit 13 comprising a number of heat transferring elements 30 formed as discs with rims 33 which are stacked so as to provide channels 31 between neighbouring elements 30 as shown in the figure. The heat transferring elements 31 are at their rims 33 sealed to the casing. By this configuration, the surfaces of the heat transferring elements 30 facing into a channel constitute the fluid contact surfaces for the fluids.

Also in this embodiment, the heat transfer unit comprising inlet and outlet stubs through which the fluid flows into and out of the unit 13. In the figure, the flow paths of the three fluids are indicated. As in FIG. 10, the unit comprising shafts 23 connected motors for rotating the impellers and these shafts are arranged in the unit by bearings and seals as described above e.g. in connection with FIG. 10.

Although all three fluids are shown to proceed all the way through the heat exchanger unit, one of the fluid may be taken of unit before it reaches the an end casing part 12 a or 12 b. In such embodiments, the part of the heat transfer unit exchanging heat between two fluids only, may be embodied similar to what is disclosed in connection with FIG. 10.

While the invention has been disclosed typically with reference to embodiments in which impellers or the like are arranged to drive at last one of the fluids through the unit, embodiment where no such pressurisation means is present may be built from the heat transferring elements presented herein. In such cases, fluid guides should be arranged to direct the fluid(s) through the unit and one or more pump(s) outside the unit be arranged to overcome the pressure loss in the unit.

FIG. 14 shows an exploded view of a further embodiment of a section of a heat exchanger unit according to the present invention. Components being the same as in the embodiment shown in FIG. 10 are provided with the same reference numbers and detailed description thereof is omitted. Similar to the embodiment shown in FIG. 10 casing parts including parts 12 a and 12 b have been left out in the figure to render the internal structure of the heat exchanger unit visible.

As in the embodiment shown in FIG. 10, the heat exchanger unit comprises a number of heat transferring elements 30 formed as discs which are stacked so as to provide channels 31 between neighbouring elements 30 as shown in FIG. 14. By this configuration, the surfaces of the heat transferring elements facing towards a channel constitute the fluid contact surface for the first and the second fluid respectively.

In this embodiment, impeller pairs (two impellers 8) are arranged in some of the channels 31. Although it is preferred to arrange the impellers of the impeller pairs symmetrically with their centres located along a radius as indicated in FIG. 14, the impellers may be arranged differently. The impellers of the impeller pairs are arranged on rotatable shafts 23. As indicated in FIG. 14, shafts 23′ drives impellers 8′ and shafts 23 drives impellers 8.

The flow paths of the fluids through the heat exchanger unit are shown by the lines marked 1^(st) and 2^(nd) in FIG. 14. As it can be realised from FIG. 14, connections are provided, typically in the casing, leading fluid from one level to another level of the unit—such connections are labelled 50 in FIG. 14.

Upon rotation of the shafts 23, each impeller in a pair of impellers generates a vortex which will interact with each other so that the vortexes generated by each impeller in an impeller pair superimpose each other resulting in a single vortex. Such a vortex will be similar to the vortex generated by a single impeller arranged with its centre coinciding with the centre of a heat transferring element.

Similarly to what was disclosed in connection with inter alia FIGS. 5 and 6, FIGS. 10, 13 and 14 show that the heat transferring elements 31 are plate shaped elements having channels for the first, the second and, FIG. 13, the third fluid respectively forming part of the flow passages through the unit and extending from one side of the heat transferring element to the other side of the heat transferring element. In FIGS. 10, 13 and 14 the channels are defined by the holes 32 a, the connection stubs 32 and, if present, the impellers 8.

The various embodiments disclosed herein have focussed on all fluids flowing from inlets to outlets (e.g. 9, 10, 15 and 16 in FIG. 8) of the heat exchanger unit. It should, however, be mentioned that connections may be provided allowing fluid to leave the unit before reaching outlets 10 and/or 16. Additionally, throttling of the fluid(s) may be provided by arranged throttling valve in e.g. the inlet(s) or outlet(s) of the unit. It should also be mentioned that heat exchanger units according to the present invention may be used with condensing fluids and non condensing fluids.

Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms “comprising” or “comprises” do not exclude other possible elements or steps. Also, the mentioning of references such as “a” or “an” etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous. 

1. A heat exchanger unit for exchanging heat between a first fluid and a second fluid, the unit comprising: a flow passage for the first fluid and a flow passage for the second fluid, the flow passages are connected to inlets and outlets of the heat exchanger unit through which the first and the second fluid flow into and out of the heat exchanger unit, more than one heat transferring elements having a first fluid contact surface and a second fluid contact surface through which surfaces heat is conducted from the first to the second fluid or vice versa, the contact surfaces form at least part of the flow passages, more than one total pressure increasing means for increasing the total pressure of more than one of the fluids at least locally in the heat exchanger unit, and a casing encapsulating the more than one heat transferring elements and all of the more than one total pressure increasing means, wherein the total pressure increasing means for the first and the second fluid are hermetically separate from each other.
 2. The heat exchanger unit according to claim 1, wherein the heat transferring element(s) are plate shaped and comprise fluid channels forming part of the flow passages for the first and the second fluids and extending from one side of the heat transferring element to the other side of the heat transferring element.
 3. The heat exchanger unit according to claim 1, wherein the first fluid contact surface of each heat transferring element is an inner surface of at least one channel provided in the heat transferring element, which channel has a channel inlet and a channel outlet.
 4. The heat exchanger unit according to claim 1, comprising a stack of at least two heat transferring elements which are connectable so that the first fluid flows from the channel outlet of one heat transferring element to the channel inlet of the consecutive heat transferring element.
 5. The heat exchanger unit according to claim 4, wherein the outlet of one channel is connected or connectable to the inlet of the consecutive channel via connection stubs, and wherein the first fluid flows from an inlet pipe to a first heat transferring element via connection stub(s) and from a last heat transferring element to an outlet pipe via connection stub(s).
 6. The heat exchanger unit according to claim 1, wherein the first fluid is pumped through the heat transferring unit by a pump arranged outside the casing of the heat exchanger unit.
 7. The heat exchanger unit according to claim 1, wherein the heat transferring element(s) are substantially disc-shaped and comprise a hole, wherein the at least one total pressure increasing means is configured to transport the second fluid flow from one side of the heat transferring element to the other.
 8. The heat exchanger unit according to claim 1, wherein the heat transferring element comprises a guide plate forming a channel leading the second fluid towards the total pressure increasing means.
 9. The heat exchanger unit according to claim 1, wherein at least a part of the casing forms a part of the flow passage for the second fluid.
 10. The heat exchanger unit according to claim 1, wherein the one or more of the total pressure increasing means are adapted to increase the pressure of the second fluid to an extent at least partially overcoming the pressure loss due to fluid flowing through the heat exchanger unit.
 11. The heat exchanger unit according to claim 10, wherein the one or more total pressure increasing means are adapted to increase the pressure of the second fluid to an extent at least overcoming the pressure loss due to the fluid flowing through the heat exchanger unit.
 12. The heat exchanger unit according to claim 1, wherein the total pressure increasing means comprises or is constituted by one or more fluid velocity inducers.
 13. The heat exchanger unit according to claim 12, wherein one or more of the fluid velocity inducers are adapted to receive one of the fluids at one velocity and deliver the fluid at a higher velocity.
 14. The heat exchanger unit according to claim 12, wherein one or more of the fluid velocity inducer(s) are arranged relatively to second fluid contact surface so that the dynamic pressure of the second fluid is substantially the same when the fluid initially contacts the second contact surface as when the fluid leaves the fluid velocity inducer.
 15. The heat exchanger unit according to claim 12, wherein one or more of the one or more fluid velocity inducers are impeller(s).
 16. The fluid exchanger unit according to claim 15, wherein the impeller(s) are impeller(s) with a motor-driven rotational motion.
 17. The heat exchanger unit according to claim 15, wherein the impeller(s) are mounted on a motor-driven shaft in such a way that the axis of rotation of the shaft and the impeller(s) are coincident.
 18. The heat exchanger unit according to claim 1, wherein the casing is a pressure carrying casing adapted to resist the pressure difference between the pressure of the fluids in the heat exchanger unit and the pressure outside the heat exchanger unit.
 19. The heat exchanger unit according to claim 1, wherein the casing or at least a part thereof is tubular shaped.
 20. The heat exchanger unit according to claim 1, wherein the casing comprises a pressurization stage said pressurisation stage being placed so that at least one of the fluids passes there through before it flows to the one or more heat transferring element(s).
 21. The heat exchanger unit according to claim 10, wherein a number of heat transferring elements are stacked with a distance between each heat transferring element so as to provide channels between two neighbouring elements, the channels being at least a part of the flow passages for the first and the second fluid, and surfaces of the heat transferring elements facing towards the channels constitute at least a part of the fluid contact surfaces, each heat transferring element is at its rim preferably sealed to a casing, and the unit comprises a number of connection stubs allowing fluid to flow from one channel to a channel located upstream of a neighbouring channel.
 22. The heat exchanger unit according to claim 21, wherein total pressure increasing means are arranged in one or more channel(s).
 23. The heat exchanger unit according to claim 21, wherein the heat transferring elements are disc shaped.
 24. The heat exchanger unit according to claim 1, wherein the heat transferring elements are adapted to be rotated.
 25. The heat exchanger unit according to claim 1, wherein at least a part of the surface of the first fluid contact surface or the second fluid contact surface are manufactured to have a roughness being smooth or rough.
 26. The heat exchanger unit according to claim 1, wherein at least a part of the first fluid contact surface or the second fluid contact surface is corrugated.
 27. The heat exchanger unit according to claim 1, wherein the material(s) of the heat transferring elements are selected from metal, composites materials, coated material, plastic, or ceramics or combinations thereof.
 28. The heat exchanger unit according to claim 1, the unit comprising one or more cassettes each containing a number of heat transferring element(s).
 29. The heat exchanger unit according to claim 28, wherein an outer housing of one or more of the cassettes forms at least a part of the casing that forms at least a part of an outer surface of the casing.
 30. The heat exchanger unit according to claim 28, wherein an outer housing of one or more of the cassettes forming at least a part of the casing abuts an interior surface of the casing.
 31. The heat exchanger unit according to claim 28, wherein one or more of the cassettes comprise(s) comprise a total pressure increasing means.
 32. The heat exchanger unit according to claim 28, wherein one or more of the cassettes are adapted to maintain or provide a rotating flow, in at least a part of one or both flow passages.
 33. The heat exchanger unit according to claim 28, wherein one or more of the cassettes is/are are adapted to receive or comprise a fluid velocity inducer, the fluid velocity inducer constituting at least a part of one or both flow passages.
 34. The heat exchanger unit according to claim 33, wherein the fluid velocity inducer is adapted to receive fluid at one velocity and deliver the fluid at a higher velocity.
 35. The heat exchanger unit according to claim 1, wherein the first and the second fluid contact surfaces are impermeable to fluid.
 36. The heat exchanger unit according to claim 1, wherein at least a part of the flow passages comprising the contact surfaces extends in a curved manner in one geometrical plane.
 37. The heat exchanger unit according to claim 1, wherein the heat exchanger unit is adapted to provide a rotating flow, such as a swirling flow past at least one or both contact surfaces. 38.-41. (canceled) 